1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer, a FAX or a multifunction device thereof, in which electrophotographic technology is utilized.
2. Description of the Related Art
A transfer member such as a transfer roller is formed of a conductive rubber or the like, and this rubber contains components such as: a residue of an initiator; a by-product produced at the time of a reaction; a low molecular component of a base polymer; and a vulcanizing agent, a softener and a plasticizer, which are added at the time of rubber roller molding. Further, when the transfer member and image carrier are left in a pressed state over a long period of time, the above-mentioned components seep (bleed) through the transfer member, and contaminate the image carrier, which might result in the formation of a contaminated region in the image carrier. Furthermore, in this contaminated region, transfer cannot be properly carried out, and an irregular image in the form of a lateral streak (i.e., a white spot image) might occur. A phenomenon in which such a white spot image occurs is promoted in accordance with the temperature of inside of an image forming apparatus in particular.
In order to eliminate the inconveniences described above, there have been disclosed a technique in which a contaminated region of an image carrier is not used as an image region as described in Japanese Unexamined Patent Application Publication No. 2003-98934 (Patent Document 1), and a technique in which a contaminated region of an image carrier is removed before image formation as described in Japanese Unexamined Patent Application Publication No. 2001-34115 (Patent Document 2).
However, if a non-image region is constantly provided on an image carrier to limit an image region as described in Patent Document 1, productivity is reduced when a large number of images are formed. On the other hand, if a contaminated region is removed before image formation as described in Patent Document 2, it is necessary to rotate a photosensitive body for a given period of time after a print instruction from a user has been received, and therefore, first print time is prolonged, which might cause the user to feel stressed.
Moreover, in order to eliminate the foregoing phenomenon, studies have also been conducted on avoidance of image formation for only a given number of sheets in a region where an image carrier and a transfer member are pressed against each other. However, since image formation is avoided for only a preset number of sheets, it is conceivable that the preset number of avoided sheets and the number of avoided sheets, which is actually necessary for removal of contamination, might be different depending on actual user's usage status and/or an environment in which an image forming apparatus is installed.